The present invention relates to methods of curing rubber in a heated mold and, more particularly, to methods of curing relatively small rubber articles in which temperature measurements are made during the curing period, and the total curing time is decremented at a rate corresponding to the temperature measurements.
Many attempts have been made to develop a system which can provide optimal time and temperature values for use in operating a mold for curing rubber articles. There are two main advantages to optimizing the cure time of rubber. First, rubber which is neither overcured nor undercured possesses the properties originally sought in determining the type of cure. Second, utilizing optimal cure times and temperatures makes the most efficient use of a curing mold and minimizes the energy required to operate it.
A problem with targeting optimum cure times and temperatures is that the cure control system may be incapable of maintaining a uniform set or target temperature for the mold, due to the cyclical operation of heating elements associated with the mold, and the fact that the mold might have to be opened during a cure thereby lowering the temperature of the mold cavity. With each increase or decrease in mold temperature, a variation in optimum cure time results.
With the advent of computer controls, it became possible to monitor the temperature of a mold and adjust the curing time and/or temperature to provide optimal cure for the particular article in the mold. Such systems typically include a mold having a temperature probe which sends a signal to a computer control. The computer control includes a timer which measures the elapsed time of cure and incorporates that value and the measured temperature value into the well-known Arrhenius Equation. An example of such a system in disclosed in the Arimatsu U.S. Pat. No. 4,542,466.
In another example, shown in the Mattson U.S. Pat. No. 4,371,483, the Arrhenius Equation is utilized to derive "cure equivalents", and the amount of cure time is determined by the number of cure equivalents generated at the particular temperatures occurring within the mold over the elapsed time of cure. A disadvantage with the aforementioned systems is that it is necessary to perform complicated calculations which can require the entry of parameters which may vary from one rubber compound to another. Accordingly, there is a need for a system and method for curing a rubber article which utilizes a simplified formula that does not require complicated calculations and entry of such parameters.